[RE-wrenches] Battery idle losses; Deka AGM

Thu Nov 3 16:27:20 PDT 2011

Hello fellow Wrenchers,

If the SI5048U was in operation with no loads and was connected to a public grid during this evaluation your findings would be correct. 

When there is no loads and the public grid is present and connected to the SI5048U it is in a Float Charge. This happens after all other charge cycles have been reached. A Float Charge is meant to keep the batteries topped off over long periods of time without overcharging the batteries. 

Internal Consumption without public grid connection and no load is at 24w. This is what you would find in a Stand-Alone Grid system.

Standby = 4w 

Float charges at 54Vdc x 1.15Adc = 62.1w  This would give us roughly the same number that was observed in the evaluation. 62.1w x 24hr = 1,490.4wh

The SI5048U can be programmed for Silent mode. This parameter can only be used if the SI5048U is operating on a public grid in the GridCharge mode not GridFeed. This parameter is for system that are predominantly in a Float Charge.  

If you have any questions please contact the SMA Service line 1-877-697-6283

SMA America, LLC
Steve Jefferson
Sr. Technical Service Specialist, Sunny Family
6020 West Oaks Blvd, Suite 300
Rocklin, CA 95765 - 3714
U.S.A.
Tel:  +1 916 625 0870
Fax: +1 916 624-2445
Service Line +1 877 697 6283 (Toll Free)
Email: steve.jefferson at sma-america.com
www.SMA-America.com

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-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jeff Irish
Sent: Wednesday, November 02, 2011 4:43 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Battery idle losses; Deka AGM

William,

I did a 2 year long study on a Sunny Island 5048 grid-intertie battery back-up system and found the SI and batteries used about 1.5kWh per day in "overhead".  The batteries were 8 Concorde AGMs 212Ah C20.  Hope that helps.  

Jeff Irish, PE
President
Hudson Valley Clean Energy, Inc.
and Adirondack Solar
13 Hook Road
Rhinebeck, NY 12572
T.845.876.3767x110
F.845.876.3912
jeff at hvce.com
Renewable Energy Systems
Solar, Wind, Geothermal
NYSERDA Eligible PV Installer
NABCEP Certified PV Installer

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Larry Crutcher, Starlight Solar Power Systems
Sent: Wednesday, November 02, 2011 2:36 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Battery idle losses; Deka AGM

Hi William,

You asked how much energy the "battery" is expect to consume. At 300 to 1200 watts perhaps you mean how much the XW's consume from the battery? The idle current? Please clarify. The battery does not consume power except for self discharge which is very small. If healthy, the 8A8D will have about 2% per month self discharge, tested by open circuit voltage. As it ages, expect that to increase. 

If you have a defective 8A8D battery(s), it will usually exhibit high surface temperature and possible valve opening during the end of the absorb cycle (57.6 volts @ 77°). Check the current going to each battery. You can do this with two clamp on DC current meters on either side of the battery in test. Current should be about 0.5 to 1 amp across the battery at the end of absorb. High current and temperature indicate a defective battery. This battery(s) will act as a load and will lower the net bank capacity at night.  BTW, I have never been able to recover an AGM from this state.

Now...some bad news. The MK 8A8D is a Deka AGM battery. We have sold and installed these 8D's for many years with few failures. Lately we are having far too many Deka's going bad in just over 1 year. Since it only has a 1 year replacement, my customers are VERY upset. After speaking with my Deka rep. last week and I have decided to advise customers to not purchase the Deka 8D's.

Larry Crutcher
Starlight Solar Power Systems

On Oct 31, 2011, at 8:20 PM, William Miller wrote:

> Friends:
> 
> I have looked on the on-line literature but I can not find this answer:  I have a client with 16 MK 8A8D batteries in 48 volt configuration feeding 3 XW inverters.  How much energy will these batteries be expected to consume at night?  We simulated darkness measured a wide range of values, anywhere from 300 watts to 1200 watts.  Has anyone measured or calculated this?
> 
> Thanks in advance...
> 
> William

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